Generally, in metallurgy, machinery, chemicals, building materials and other production industries and during energy conversion process of boilers and furnaces or the like, a huge amount of dust gas is generated, and an environmentally dust removing process is required. Currently, the major environmentally dust removing processes comprise 3 types of processes of water spraying dedusting, bag dedusting and electrostatic dedusting. Among them, the bag dedusting is mainly used, and the utilization ratio is more than 80%, which will increase in the future. Further, the bag dust remover mainly comprises an outer-filer type bag or filter cartridge dust remover, the utilization ratio of which is more than 90%.
The traditional outer-filer type bag or filter cartridge dust remover always adopts the “online pulse-jet deashing” process, during which the dust remover performs dedusting and deashing simultaneously. In this case, the internal space of the dust remover body and the external space of the pipeline are communicated without being blocked and with airstream flowing therebetween. The basic working principle thereof is as follows.
During the filtration process of the dust remover, due to a negative pressure, an accumulation shelf layer (dust layer) is generally formed on the filter cloth surface. At the beginning, the accumulation shelf layer (dust layer) is very thin and has a small resistance value. As the dedusting time elapses, its thickness increases, and thus its resistance value increases. Since the accumulation shelf layer (dust layer) is generally uniformly distributed on the filter cloth surface, it serves to supportively enhance the filtering accuracy of the filter cloth.
When the accumulation shelf layer (dust layer) reaches a certain thickness, if the sum of the resistance value of the accumulation shelf layer and other additional resistance values of the dust remover reaches the designed resistance value 1,000-1,200 Pa of the dust remover, the dust remover may start up the pulse-jet deashing device to perform pulse-jet deashing. At this time, the filtration chamber is in an open space under the negative pressure, that is, it is not blocked from the external space, and an airstream flows therebetween.
The purpose of each pulse-jet deashing is to break the already formed accumulation shelf layer (dust layer) having the certain thickness so as to make it thinner and thus to obtain a new accumulation shelf layer (dust layer) having a reduced resistance value. Therefore, the accumulation shelf layer (dust layer) is often broken by the pulse-jet deashing, and after the accumulation shelf layer (dust layer) is regenerated, it is broken by the pulse-jet deashing again. Such process is repeated as a traditional dedusting mode of “accumulation shelf layer (dust layer)—pulse jet breaking accumulation shelf layer (dust layer)—accumulation shelf layer (dust layer).”
Therefore, the traditional “online pulse-jet deashing” outer-filer type bag or filter cartridge dust remover has 3 major insurmountable defects as follows:
1. since the pulse-jet deashing is performed within the open space under the negative pressure, the dust proceeds in three directions after being separated from the bag or the filter cartridge surface: a part (thick, heavy, caking) falls directly into the ash bucket; a part flows with the airstream and attaches to the adjacent bag or filter cartridge surface; and a part also attaches to the original bag or filter cartridge surface after the jetted high-pressure airstream disappears. Therefore, the dust on the filter cloth cannot be cleaned completely.
2. at the moment that the high-pressure gas pulse-jet deashing is performed, micropores of the filter cloth have to be expanded, and at the moment that the high-pressure airstream disappears and a negative pressure is created, many dust particles may pass through the expanded micropores, and thus the filtration accuracy and efficiency of the filter cloth are reduced. Since the frequency at which the pulse-jet deashing is performed is high, the influence of such moments may be accumulated to an extent that the filtration accuracy and efficiency of the filter cloth are severely affected.
3. as described above, first, since the purpose of each pulse-jet deashing is to break the accumulation shelf layer (dust layer), the accumulation shelf layer (dust layer) has no continuity; second, after the pulse-jet deashing, the new dust and the old dust always arrive at the filter cloth surface at the same time to form a new accumulation shelf layer (dust layer), thus the sizes of the dust particles forming the accumulation shelf layer (dust layer) are not sorted; and third, after each pulse-jet deashing, a new balance of resistance value is required again, and thus the thickness of the accumulation shelf layer (dust layer) is substantially constant, which is not controllable.
As described above, as to the supportive enhancement of the filtration accuracy and efficiency of the filter cloth by the accumulation shelf layer (dust layer), it is counteracted by an inherent defect of the micropore expansion of the filter cloth at the moment of on-line pulse-jet deashing and also by an inherent defect of the thickness-uncontrollable, discontinuous and unsorted accumulation shelf layer (dust layer).
To solve the problem of incomplete cleaning of the filter cloth, an invention patent application entitled “Closed pulse dust remover and dedusting method thereof,” (Application No: 201310007537.6) and a utility model entitled “Off-line cleaning flat bag type dust remover” (Patent No: 201220070395.9) propose a solution in which a valve is provided at the outlet of the purified gas, and the purpose thereof is to achieve an off-line cleaning. However, this solution cannot generate a thickness-controllable, sorted and continuous super accumulation shelf layer.